The present invention relates, in general, to the field of magnetoresistive ("MR") devices and methods for fabricating the same. More particularly, the present invention relates to magnetoresistive devices and processes for manufacturing the same for use as an MR sensor which exhibits improved Barkhausen noise suppression characteristics.
Magnetoresistive sensors or heads are known to be useful in reading data from a magnetic surface with a sensitivity exceeding that of inductive or thin film heads. In operation, a MR sensor is used to detect magnetic field signal changes from a magnetic surface due to the fact that the resistance of the MR sensor changes as a function of the direction and amount of magnetic flux being sensed. It is also generally known that for an MR sensor to function effectively, it must be subjected to a transverse bias field to linearize its response. Various techniques for effectuating such transverse biasing are known including current shunt biasing and soft adjacent film biasing. The transverse bias field is applied normal to the plane of the magnetic media and parallel to the surface of the MR sensor.
It is also known that an MR sensor may be utilized in conjunction with a longitudinal bias field extending parallel to the surface of the magnetic media and parallel to the major axis of the MR sensor. Stabilization of MR sensors by means of a longitudinal bias field is necessary for their application with high track density disk files in order to suppress Barkhausen noise. Barkhausen noise results from unstable magnetic properties such as multi-domain activities within the MR element.
With respect to the application of a longitudinal bias field for the suppression of Barkhausen noise in an MR sensor, a number of patents have issued in this area, primarily dealing with "exchange bias" through use of an antiferromagnet coupled in some manner to the MR device. Exemplary of these patents are U.S. Pat. No. 4,663,685 "Magnetoresistive Read Transducer Having Patterned Longitudinal Bias" issued May 5, 1987; U.S. Pat. No. 4,713,708 "Magnetoresistive Read Transducer" issued Dec. 15, 1987; U.S. Pat. No. 4,809,109 "Magnetoresistive Read Transducer and Method for Making the Improved Transducer" issued Feb. 28, 1989 and U.S. Pat. No. 4,825,325 "Magnetoresistive Read Transducer Assembly" issued Apr. 25, 1989. With these exchange bias MR sensors, the materials in current use to form an antiferromagnet, such as manganese and its alloys, are known to be highly reactive and have poor thermal characteristics.
In an attempt to solve the problems inherent with the use of an antiferromagnet to provide longitudinal bias, a number of patents and publications have described the use of an MR sensor stabilized through the use of permanent magnet films. Exemplary of the techniques known are those described in U.S. Pat. No. 4,639,806 "Thin Film Magnetic Head Having a Magnetized Ferromagnetic Film on the MR Element" issued Jan. 27, 1987; Hunt, R. P. and Jaecklin, A. A., "Composite Films as a Domain-Wall Barrier", Journal of Applied Physics, volume 37, no. 3, Mar. 1, 1966; European Patent Application No. 0,375,646 published Jun. 27, 1990 and European Patent Application No. 0,422,806 published Apr. 17, 1991. Some of the previous designs using permanent magnets for Barkhausen noise suppression by application of a longitudinal bias to the MR sensor have been shown to be generally not suited for use with closely coupled magnetic shielding layers. The remainder of the techniques previously described are not readily implementable and reproducible.